In general, fluoroepoxides can be prepared by epoxidation of fluoro-olefins. Due to the fact that fluoro-olefins have chemical properties very different from hydrocarbon-type lefins such as propylene or chlorinated hydrocarbon-type olefins such as allyl chloride, however, it is difficult to epoxidize fluoro-olefins in a manner similar to propylene or allyl chloride.
For example, both propylene and allyl chloride are epoxidized by a chlorohydrin process which effects cyclization with an alkali via chlorohydrin. On the other hand, in the epoxidation of fluoro-olefins by the chlorohydrin process, chlorohydrin is unstable and decomposes to carbonyl compounds so that it is impossible to change it into fluoroepoxides.
Accordingly, a variety of processes have heretofore been proposed for epoxidation of fluoro-olefins which are different from the process for the epoxidation of hydrocarbon-type olefins or chlorinated hydrocarbon-type olefins. However, none of these processes are industrially advantageous processes for preparing fluoroepoxides.
A process as described in U.S. Pat. No. 3,358,003 which comprises oxidizing fluoro-olefins to fluoroepoxides in an alkaline hydrogen peroxide medium, a process as described in U.S. Pat. No. 3,536,733 which comprises oxidizing fluoroolefins to fluoroepoxides with oxygen in the presence of an inert solvent, etc. are heretofore known as typical processes for preparing fluoroepoxides. However, it is impossible to obtain fluoroepoxides in high yield since, in any of these processes, it is difficult to control the reaction, it is difficult to prevent the decomposition of the formed fluoroepoxides, or large quantities of side-products are by-produced, etc. Further, a high conversion of fluoro-olefins results in reduction in selectivity of fluoroepoxides. In order to effectively use fluoroolefins, it is thus necessary to discontinue the reaction at a low fluoro-olefin conversion separate the unreacted fluoro-olefins from fluoroepoxides, recover and re-use them. However, the boiling points of fluoroolefins are generally very close to those of fluoroepoxides so that it is difficult to separate both from each other through distillation, and special procedures are thus required for the separation. As typical examples for such procedures, a method which comprises reacting the unreacted fluoro-olefins with bromine to convert them into dibromo-compounds having high boiling point and then separating the dibromo-compounds from fluoroepoxides, and methods for separation through extracive distillation as described in U.S Pat. Nos. 3,326,780 and 4,134,796 have been proposed. However, these methods are complicated and seriously increase the production costs of fluoroepoxides.
On the other hand, it is known in a process comprising oxidation using hypochlorites that fluoroepoxides are produced from fluoro-olefins in a system where a polar solvent such as acetonitrile, diglime, etc., is incorporated into a hypochlorite aqueous solution (IZV. AKAD. NAUK. SSSR, SER. KHIM., 79 (11) 2509). The study of this process by the present inventors revealed that the selectivity of fluoroepoxides was poor and fluoroepoxides could not be obtained in high yield. Although it is not completely understood, it is assumed that the formed fluoroepoxides would easily react with water and decompose under alkaline conditions since the reaction system is a homogeneously mixed system of a polar solvent and an alkaline hypochlorite aqueous solution. In addition, a complicated step of recovering the polar solvent from the reaction system after completion of the reaction is also required in this process. In view of the foregoing, it can be understood that the process of this reaction type cannot be used as a practical technique for the preparation of fluoroepoxides.
As a result of extensive investigations attempting to overcome such drawbacks in the prior art processes and find a process for preparing fluoroepoxides in a simple manner and high yield, the present inventors have found that when the reaction is carried out in a two phase system of an aqueous phase and an organic phase using hypochlorites as oxidizing agents in the presence of at least one phase transfer catalyst selected from the group consisting of quaternary ammonium salts, quaternary phosphonium salts, quaternary arsonium salts, sulfonium salts and lipophilic complexing agents for cations contained in hypochlorites, fluoroepoxides are obtained from fluoro-olefins in high yields.